Field of the Invention
The present invention relates to a technique of performing superimposed projection of a plurality of videos.
Description of the Related Art
There is known a multi-projection system that displays a video on a large screen or a non-flat projection surface by combining a plurality of projection video display devices (to be referred to as “projectors” hereinafter). Projection methods in the multi-projection system include stack projection in which a plurality of projectors project the same video on the same projection surface, and multiple projection in which respective projectors perform projection of respective regions obtained by dividing one video and the divided regions are joined on the projection surface. In either projection method, the projection surface has an overlapping region where a plurality of projected images overlap each other. In the stack projection, superimposed projection of the same video is performed, so the entire projected image corresponds to an overlapping region. To the contrary, in the multiple projection, superimposed projection is applied to part of adjacent projected images in order to make the joint of a video less conspicuous. In the multiple projection, an overlapping region exists at the joint of the projected images.
In the overlapping region, the projected positions of respective videos need to coincide with each other. If a projected position has a displacement, the resolution of the entire projected image decreases, degrading the image quality. Main causes of the displacement of a projected position by a plurality of projectors are temporal change of an optical component, deformation of an optical component and support member by heat of a light source, movement of a projector housing by vibrations of a member, and the like. Since the projector enlarges and displays a video by projection, even a small change of the optical component or the like appears as a large displacement on the projection surface. For example, a change of the optical component occurred by the temporal change appears as a larger displacement of the projected position on the projection surface. Since the temporal change does not have homogeneity, the displacement amount of the projected position is spatially and temporally inhomogeneous.
There has been proposed a technique of suppressing generated image quality degradation in accordance with a displacement between the positions of a plurality of videos in an overlapping region in a multi-projection system. Japanese Patent No. 5298738 (literature 1) discloses a technique of performing image correction corresponding to the displacement of a projected position using a detection pattern. Japanese Patent Laid-Open No. 2011-211693 (literature 2) discloses a technique of enabling image correction corresponding to the displacement of a projected position even during projection of a video using an invisible detection pattern.
However, since the technique disclosed in literature 1 executes correction using a detection pattern of visible light, correction corresponding to the displacement of a projected position cannot be executed during projection of a video and adaptive correction is impossible. The technique disclosed in literature 1 executes uniform image correction on an entire projected image. If this technique is applied to a projected image having an inhomogeneous displacement, a region where correction is insufficient or excessive is generated. Therefore, the technique disclosed in literature 1 has a poor image quality degradation suppressing effect for a projected image having an inhomogeneous displacement.
The technique disclosed in literature 2 executes correction using an invisible detection pattern, and can execute image correction corresponding to the displacement of a projected position even during projection of a video and can execute adaptive correction. However, as in literature 1, the technique disclosed in literature 2 executes uniform image correction on an entire projected image, and has a poor image quality degradation suppressing effect for a projected image having an inhomogeneous displacement.